34
8. RA-4/4A Power Supply Troubleshooting
FIGURE 8-5 - CONVERTER
FROM SWITCHING B+
FROM VCC SOURCE
D6015/K
FROM IC6003/9
E1 OSCILLATOR
FROM IC6003/10
E2 OSCILLATOR
D6031
VCC
+12V
VDD
HIN
LIN
SD
VSS
GND
HO
VB
VS
LO
VCC
IC6002
DRIVER
IR2112
VDD
HIN
LIN
SD
VSS
GND
HO
VB
VS
LO
VCC
IC6004
DRIVER
IR2112
F6002
C6019
C6020
D6016
C6018
C6021
C6030
C6032
D6025
C2029
C6037
D6026
MTZJ
-20C
FB6003
D6028
MTZJ
-20C
FB6002
R6025
D6019
MTZJ
-20C
D6022
MTZJ
-20C
FB6001 R6024
D6017
MTZJ
-20C
D6021
MTZJ
-20C
FB6004
D6021
MTZJ
-20C
R6035
R6026
Q6009
D6030
MTZJ
-20C
R6036
R6038
Q6010
SWITCHING B+
R6026
Q6007
R6027
Q6008
C6026
C6025 C6022
C6034
C6033
C6023
SWITCHING B+
T6002 PIT
T6001 PIT
8.5TVP14
5/22/02
9
10
12
11
13
2
7
6
5
1
3
9
10
12
11
13
2
7
6
5
1
3
4
2
8
10
12
1
3
12
10
11
15
13
14
18
16
17
8
7
9
Unit Will Not Power Up
Look at the timer LED. If it is blinking once a second, the standby supply is working. The main and inrush current
relays will now become an important tool in deciding where to go next.
No relay clicks heard: There should be two, distinct, rapid clicks heard. If none are heard, troubleshoot the circuit
starting from the relay high command from the CPU through the VCC switch circuitry and even the main relay
itself. Refer to Figure 8-3 to troubleshoot this circuit.
Relay clicks once: If a relay click is heard, it is very important to listen carefully for
two rapid clicks
. They should
be less the one-half of a second apart. This verifies the inrush current relay is engaging. If only one, and not two,
rapid clicks are heard, the unit will power up for a short period and then the oscillator will stop. The main relay will
still be engaged and there will be no other indicators as to what is wrong. This is the symptom of the inrush relay
protection. Check for a defective relay or loss of 14V supplied by Q6106 on the 16.5V line on the secondary of
T6001. One might think that a failure of the oscillator circuit could cause this symptom but several of the
secondary voltages are monitored by the protect circuits and the relay click sequence will differ as shown next.
It is very important to verify this test as it can lead the technician to the wrong areas.
Two rapid relay clicks: The presence of the two clicks indicates the power supply is oscillating. One item that can
produce the symptom of a dead set is the loss of 12V from IC501 on the A board. This would prevent the
horizontal oscillator from running and may mimic the symptom of a dead unit.